1. Field of the Invention
The present invention relates to cross-sectional image generating apparatuses and three-dimensional printing systems.
2. Description of the Related Art
A three-dimensional printing apparatus to print a three-dimensional object by sequentially stacking layers each having a predetermined cross-sectional shape is known in the related art. In one example, a three-dimensional printing apparatus known in the related art includes: a tank storing powdery materials; and a printing head to discharge a binder onto the powdery materials stored in the tank. The three-dimensional printing apparatus sequentially stacks layers formed by curing the powdery materials with the binder. To print a three-dimensional object in full color, such a three-dimensional printing apparatus may further include an ink head to discharge ink onto the layers formed.
Printing a three-dimensional object in this case involves determining, in accordance with a cross-sectional image representing a predetermined cross-sectional shape, a region onto which the binder is to be discharged and a region onto which the ink is to be discharged. A cross-sectional image to be used for printing a three-dimensional object is generated using a computer program. An internal portion of a three-dimensional object may be visually unrecognizable from outside. In such a case, coloring an entirety of the internal portion in printing the three-dimensional object in full color leads to ink wastage and prolonged printing time. A conceivable solution to this problem is to set a colored pixel and a non-colored pixel in a cross-sectional image. The colored pixel is a pixel having any desired width and in the vicinity of the outline of a cross-sectional shape. The non-colored pixel is a pixel located inward of the colored pixel. Specifically, the non-colored pixel is a pixel located inside a figure defined by a line provided by reducing the outline of the cross-sectional shape. As used herein, the term “reducing” or “reduction” refers to reducing the size of a figure (which is a cross-sectional shape in this case) without degrading topological properties. The term “outline” refers to a boundary between white pixels and black pixels in a binarized cross-sectional image.
The following description discusses an example where the outline of a cross-sectional shape 101 illustrated in FIG. 13 is reduced. FIG. 13 illustrates a cross-sectional image 104 including: the cross-sectional shape 101; printed pixels 102 located inward of the cross-sectional shape 101; and non-printed pixels 103 located outward of the cross-sectional shape 101. FIG. 14 illustrates a mask 105 to reduce the cross-sectional shape 101 by two pixels. The mask 105 includes: a center pixel 107; and eight adjacent pixels 106 located around the center pixel 107. A process for reducing the outline of the cross-sectional shape 101 involves: placing the mask 105 such that the center pixel 107 of the mask 105 overlaps with each selected one of the pixels in FIG. 13; and regarding the pixel corresponding in position to the center pixel 107 as the non-printed pixel 103 when at least one of the adjacent pixels 106 of the mask 105 overlaps with the non-printed pixel 103. Repeatedly performing this process provides, as illustrated in FIG. 15, a cross-sectional image 109 including a reduced cross-sectional shape 108 defined by a line provided by reducing the outline of the cross-sectional shape 101. The printed pixels 102 in FIG. 15 include: pixels located outward of the outline of the reduced cross-sectional shape 108; and pixels located inward of the outline of the reduced cross-sectional shape 108. The printed pixels 102 located outward of the outline of the reduced cross-sectional shape 108 are set to be colored pixels 110. The printed pixels 102 located inward of the outline of the reduced cross-sectional shape 108 are set to be non-colored pixels 111.
Suppose that the outline of the cross-sectional shape 101 illustrated in FIG. 16 is reduced using the mask 105 illustrated in FIG. 14. In this case, one or some of the non-colored pixels 111 after reduction of the outline may be cut off from the other non-colored pixels 111 depending on the resolution (i.e., the number of pixels per unit area) of the image, and a plurality of groups of the non-colored pixels 111 may exist (see FIG. 17). Intermingling of the colored pixels 110 with one or more of the non-colored pixels 111 as illustrated in FIG. 17 may make it impossible to suitably print a layer and may degrade the quality of the resulting three-dimensional object. Thus, printing a high-quality three-dimensional object desirably requires a cross-sectional image in which colored pixels are not intermingled with unnecessary non-colored pixels.